While today's telecommunication transmission networks rely mainly on optical transmission, internal signal processing in the network elements of a transmission network is still electrical in most cases.
The recent definition of the multiplexing principles and bitrates of an Optical Transport Network (ITU-T G.709) introduces a three level hierarchy with bitrates of 2.7 Gbit/s, 10.7 Gbit/s and 43 Gbit/s. Therefore, equipment is required for electrically processing these high bitrate signals. In particular, a need exists for an optical crossconnect for establishing cross-connections in an optical transport network. An optical crossconnect is a kind of switch with a huge number of I/O ports allowing to establish connections from any to any of these 110 ports. Internally, most optical crossconnects operate electrically, as all-optical switching still provides a number of drawbacks and envolves certain system limitations. An optical crossconnect, internally operating electrically, has thus to switch a number of asynchronous electrical signals at different bitrates from any input to any output port. This requires high speed integrated electrical switching circuits in order to form large integrated electrical switching matrices.
Generally, CMOS technology is preferred today for integrated circuits, but is not suited for high bitrate applications above 2 Gbit/s. On the other hand, bipolar integrated circuits based on SiGe technology would in principle be suitable for applications of up to 20 Gbit/s but have high power consumption. Typically, bipolar integrated circuits typically operate at an operating voltage of 5V. In particular, each circuit element (e.g., switch, multiplexer or the like) in a bipolar circuit has two truncs. When the circuit element is in operation, a constant current is switched from one trunc to the other. Since the constant current always runs through one of the truncs, such bipolar circuits have a high power consumption and great heat dissipation, which makes them unattractive for large switching matrices designed for high bitrate applications.
It is therefore an object of the present invention to provide a basic switching circuit suitable for high bitrate applications of 10 Gbit/s or more, and which does not suffer from the aforementioned drawbacks of existing integrated circuits.